Specific examples of a device provided with a positive electrode and a negative electrode, in which a reaction represented by the following formula (1) is performed on aside of the positive electrode, include a metal-air secondary battery and an alkaline water electrolysis apparatus.4OH−→O2+2H2O+4e−  (1)
The metal-air secondary battery is a secondary battery in which a metal such as Zn, Li, Al and Fe is used as an active material at the negative electrode, and oxygen in air is used as an active material at the positive electrode. The metal-air secondary battery is small and can achieve high capacity, and expected in an application to power supply for an automobile, portable power supply, stationary power supply or the like.
A charge reaction and a discharge reaction in the metal-air secondary battery in which Zn is used at the negative electrode are represented as described below.
(Charge Reaction)
Positive electrode:4OH−→O2+2H2O+4e−
Negative electrode:ZnO+H2O+2e−→Zn+2OH−
(Discharge Reaction)
Positive electrode:4OH−→O2+2H2O+4e−
Negative electrode:Zn+2OH−→ZnO+H2O+2e−
Moreover, an electrode reaction in the alkaline water electrolysis apparatus is represented as described below.
Positive electrode:4OH−→O2+2H2O+4e−
Negative electrode:2H2O+2e−→H22OH−
However, the metal-air secondary battery has a problem of reduction of energy conversion efficiency caused by high reaction overpotential at the positive electrode during charging and discharging, and has not been extensively applied yet.
Moreover, the alkaline water electrolysis apparatus also faces a problem of large energy loss caused by the high reaction overpotential at the positive electrode.
Patent Literature 1 discloses an air electrode of a metal-air secondary battery, which is produced by mixing nickel powder on which iridium and/or an iridium oxide is supported, nickel powder on which an oxygen reduction catalyst such as platinum is supported, and a binder, and molding the resultant mixture.
Moreover, Non-Patent Literature 1 presents a report in which, if LaNiO3 being one kind of perovskite oxide is used as a positive electrode catalyst, reaction overpotential during discharging can be reduced to 320 mV.